As a flat panel type display device (flat display), a liquid crystal display device (LCD), an organic electro luminescence (EL) display device, or the like is known. In addition, as one of drive methods of the flat panel type display device, there is an active matrix method. In a display device of the active matrix method (type), a unit pixel (hereinafter, may be simply referred to as “pixel”) including a light emitting unit (light emitting element) includes at least a writing transistor that writes a signal (for example, PTL 1).